Prosthetic device

ABSTRACT

The present invention relates to a method and a device for alleviating and/or preventing conditions relating to damaged joints involving articulating surfaces. In a first aspect the present invention relates to a prosthetic device for insertion into a joint cavity of a joint of a vertebrate, such as a human, said device consisting of a biocompatible material comprising at least a first polymeric component and a second polymeric component, wherein the chain length of the first polymeric component is longer than the chain length of the second polymeric component, the polymeric components in particular being polyethylene, polypropylene and/or polyvinylpyrrolidone. The device may be used for establishing slidability and/or distributing pressure in a joint of a vertebrate such as a human, by inserting into the joint cavity of the joint a prosthetic device, preferably a prosthetic device as defined in this invention, capable of locking itself to an intra-articular component and thereby being fixed or retained in the joint cavity in a manner which is substantially non-invasive with respect to cartilage and bone natively present in the joint cavity. The device may be formed by moulding, whereby it is possible to adapt the form of the device to the joint needing alleviation. Also the device may be formed with a hole or a slit to fit into the joint and lock the device around intra-articular components. A further aspect of invention relates to a method for introducing the prosthetic device into a joint, such as a method comprising locking the device to an intro-articular component, thereby fixing or retaining the device in the joint cavity in a manner which is substantially non-invasive with respect to cartilage and bone natively present in the joint cavity. Also the invention relates to an instrument for inserting a prosthetic device according to the invention, comprising means for deforming the prosthetic device into a reduced volume or a slender shape and means for grasping the intra-articular component to which the device is capable of interlocking.

FIELD OF INVENTION

[0001] The present invention relates to a method and a device foralleviating and/or preventing conditions relating to damaged jointsinvolving articulating surfaces.

GENERAL BACKGROUND

[0002] At present, joint damage, such as cartilage damage, is treated byreplacing the joint with an artificial joint. However, seriouscomplications are caused by the replacement of artificial joints, inparticular a high occurrence rate of loosening problems resulting inbreakage of the bones around the artificial joint.

[0003] In particular, the invasive character of the fixation of theprostheses such as anchoring of the prosthesis with screws and pinsresults in numerous side-effects such as risk of infection, loosening asmentioned above, damage on excising bone due to interruption of bloodsupply and necrosis.

[0004] A device for replacement within a joint should preferably enablethe normal function and movements of the joint. Weight-bearing joints,in which movement in more than one direction takes place, are normallyrather difficult to replace.

[0005] A prosthetic device should enable the normal movement of thejoint. During walking, the normal movement of for example the hip jointcorresponds to about 37°-41° flexion/extension, 2°-14°adduction/abduction and a rotation of about 2°-16°. During movement fromstanding to sitting position a flexion of hip joint corresponds to amovement from 0 to 90 degrees. When studying the movement of femoralcaput to the acetabulum the latter movement includes a rotation of 90degrees.

[0006] So far, no satisfactory device for placement within a joint hasbeen achieved in the prior art.

SUMMARY OF THE INVENTION

[0007] In a first aspect the present invention relates to a prostheticdevice for insertion into a joint cavity of a joint of a vertebrate,such as a human, said device consisting of a biocompatible materialcomprising at least a first polymeric component and a second polymericcomponent, wherein the chain length of the first polymeric component islonger than the chain length of the second polymeric component.

[0008] The invention disclosed furthermore relates to a prostheticdevice for insertion into a joint cavity of a joint of a vertebrate suchas a human, wherein the body of the device comprises a polymer material,and wherein the device is non-invasive with regards to theintra-articular components when the device is in the joint cavity, saiddevice being adapted to alleviate conditions associated with worncartilage;

[0009] and in a third aspect the present invention provides:

[0010] a prosthetic device for insertion into a joint cavity of avertebrate such as a human, wherein the body of the device comprises apolymer material, and wherein the device comprises a hole extendingthrough the body of the device.

[0011] By the term “non-invasive” is meant that the device is preferablynot attached to joint components through the use of screws, stitches orthe like.

[0012] Also, the invention relates to a method for introducing aprosthetic device into a joint, such as a method comprising locking thedevice to an intra-articular component, thereby fixing or retaining thedevice in the joint cavity in a manner which is substantiallynon-invasive with respect to cartilage and bone natively present in thejoint cavity.

[0013] Another aspect of the invention is an instrument for inserting aprosthetic device according to the invention, comprising means fordeforming the prosthetic device into a reduced volume or a slender shapeand means for grasping the intra-articular component to which the deviceis capable of interlocking.

[0014] Yet a further aspect of the invention relates to the use of aprosthetic device for establishing slidability and/or distributingpressure in a joint of a vertebrate such as a human, by inserting intothe joint cavity of the joint a prosthetic device, preferably aprosthetic device as defined in this invention, capable of lockingitself to an intra-articular component and thereby being fixed orretained in the joint cavity in a manner which is substantiallynon-invasive with respect to cartilage and bone natively present in thejoint cavity.

[0015] Another aspect relates to a method for establishing slidabilityand/or pressure distribution in a joint of a vertebrate such as a human,comprising inserting into the joint cavity of the joint, a prostheticdevice, preferably a prosthetic device as defined herein, which iscapable of locking itself to an intra-articular component and therebybeing fixed or retained in the joint cavity in a manner which issubstantially non-invasive with respect to cartilage and bone nativelypresent in the joint cavity.

[0016] Yet another aspect is a kit comprising:

[0017] a) an intra-articular prosthetic device for a joint having

[0018] a.1) a spacer function and/or capability to exert pressuredistribution and/or sliding/rotating movement of the joint by internalmovement of the device by means of a resilient member, and

[0019] a.2) a locking mechanism adapted to fix the device to anintra-articular component by means of an element of the devicesurrounding the component in such a manner that displacement of thedevice is limited by inter-locking with the component; and

[0020] b) an instrument for inserting the prosthetic device into a jointcavity.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The device and units are designed to occupy at least part of theintra-articular cavity to partly or completely fill the role of naturalcartilage within a joint. The device or its units may be designed so asto occupy the whole of the cavity or merely a portion of theintra-articular cavity, such as the portion of the cavity wherecartilage is worn or where much of the pressure is exerted. The deviceand its units may radially encircle an intra-articular componentspanning a longitudinal axis of the cavity or may occupy one or moreportions of the cavity laterally removed from the intra-articularcomponent and its axis.

[0022] The device and units may be designed not to interfere and to benon-invasive with regards to intra-articular components when the deviceis in the joint cavity by means such as a slit in the body of thedevice.

[0023] Moreover, non-interference of the intra-articular components maybe achieved by a hole which runs through the body of the device; that isto say the device may comprise a hole through which intra-articularcomponents may pass. When loading the device, the slits may serve topass intra-articular components through the body of the device. Theslits in this embodiment run from the periphery of the body of thedevice to the hole through which the intra-articular components passafter the device is implanted or loaded.

[0024] Typically, and to at least some extent, the device is adapted inits structure and/or material composition to alleviate conditionsassociated with worn cartilage by providing a spacer function and/or toexert pressure distribution in the joint when the joint is loaded and/orto provide at least part of the sliding/rotating movement of the jointby internal movement of at least part of the device.

[0025] It is also an object of the present invention to provide a methodfor non-invasive locking of a device within a joint. In addition, themethod is independent of use of cement or bony ingrowth of the device.

[0026] A still further object of the present invention is to provide akit for use in the method for non-invasive locking of a device within ajoint.

[0027] It is also an object of the present invention to provide a methodfor preventing damage between mating surfaces or articulating surfaceswithin a joint such as between the femoral head and the acetabulum of ahip joint.

[0028] A more specific object of the present invention relates to aprosthetic device for insertion into a joint cavity of a joint of avertebrate such as a human, the device is being adapted to provide aspacer function and/or to exert stress distribution in the joint whenthe joint is loaded and/or to provide at least part of thesliding/rotating movement of the joint by internal movement in thematerial of at least part of the device, the device being capable oflocking itself to an intra-articular component and thereby being fixedor retained in the joint cavity in a manner which is substantiallynon-invasive with respect to cartilage and bone natively present in thejoint cavity.

[0029] Physical-Structural Features of the Device

[0030] The physical-structural features of the device relate to thesize, form or shape of the device as well as the structural componentsand design components of the device.

[0031] Size and Shape

[0032] The overall shape of the device is such that it substantiallyfits into the excising anatomical dimensions of the joint. In general,the size and shape of the device are such that the device fits into theintra-articular cavity in that it may partially or fully occupy thespace defined by the cavity. For some of the joints it is preferred thatthe extent of the device, when positioned in the joint cavity, is largerthan the normal extent of cartilage on the bone end in that joint.

[0033] In a preferred embodiment, a hole runs through the body of thedevice to allow intra-articular components to traverse the body of thedevice and thus be surrounded by the device.

[0034] In this embodiment, the device may be construed in a liberalsense as essentially torus-shaped in that the device can be of aplurality of geometrical shapes, symmetrical and asymmetrical,comprising a hole which runs through the body to create an internaltubular passage through which intra-articular components may pass.

[0035] The device may also be ball-shaped, disc-shaped, spherical,globular-shaped, cup-shaped, cone-shaped, ring-shaped, cylindrical andhave convex, concave, or flat surfaces. Accordingly, the body of thedevice shape can e.g. be in the form of a horseshoe, a curl,ring-shaped, circular or semicircular so as to be suitable for fittinginto the anatomical dimensions of the particular joint. Furthermore, thedevice may be unsymmetrical.

[0036] The body of the device may be of a geometrical shape comprising asurface having the form of body shaped by rotating a circle about acoplanar axis which does not intersect the circle. It may beball-shaped, disc-shaped, globular-shaped, cup-shaped, cone-shaped,ring-shaped, cylindrical and may comprise convex, concave, or flatsurfaces. In some aspects it is characterised in that it comprises ahole extending from one surface of the body of the device to the same oranother surface, creating an internal tubular cylinder. This internaltubular cylinder may be straight if the hole extended to two parallelsurfaces, curved if the hole extends to perpendicular surface, U-shapedif the hole extends to two parts of the same surface or a combination ofone or more of these internal shapes and thus tortuous.

[0037] Certainly, given that the overall shape of the device is suchthat it substantially fits into the excising anatomical dimensions ofthe joint, it is anticipated that the body of the device may beasymmetrical or of no definable shape so as the fill the intra-articularcavity, to allow for the movement of the intra-articular componentsduring the flexing of the joint, to support intra-articular componentsor to support matter which form the walls of the cavity.

[0038] It is preferable that the shape of the device is such that itdoes not impede the normal functioning of the joint and its components.

[0039] It is particularly anticipated that the body of the device may beasymmetrical or of no definable or uniform shape when the device is foruse in a hip joint. Alternatively, the shape of the device may be suchthat it resembles the native cartilage, or part thereof, naturallypresent in the joint cavity.

[0040] Accordingly, in the case of a hip joint, the shape of the deviceis preferably such that it fits into the existing space of the jointcavity comprising ligamentum capitis femoris, the “walls” of the spacebeing defined by the concave shape of the acetabulum and by the convexshape of the femoral head.

[0041] Moreover, the overall shape of the device may be a result of anassembly of more than one units of the device, such as the assembly oftwo or more rings of different sizes stacked upon each other so as toform a cone-shaped device. The assembly of units may be done in vivo orex-vivo.

[0042] Furthermore, in preferred embodiments, the overall shape is suchthat the device is capable of locking itself to an intra-articularcomponent if present in said joint and thereby being fixed or retainedin the joint cavity. When the intra-articular component is a ligament,the shape is such that the ligament is surrounded or substantiallysurrounded by the device.

[0043] However, the overall shape of the device may have any other formas long as the material is of such a character that the device whenpresent in situ fits into the joint cavity, for example due to elasticaldeformation of the device.

[0044] Preferably, the elastical deformation of the device is such thatthe presence of ligamentum capitis femoris results in a shape leavingroom for the ligamentum. Otherwise, the surface of the upper part of thedevice facing the acetabular cavity may comprise a groove embedding theligament.

[0045] Typically, the shape of the device is formed from a moulding ofits materials or from a casting process. It may alternatively be theresult of a framed structural construction or skeletal assembly. It istypically solid in that the body of the device is not hollow but rathersuch that the material of the device comprises all or essentially all ofthe space between two surfaces. The moulding, casting, construction orassembly may form a device into a uniform or non-uniform shape.

[0046] The device is essentially uniform in its stiffness orcompressibility. However, when loaded, the material may have a tendencyto deform in such a way that the locking mechanism is altered. This mayoccur if the element adapted to surround the ligament, when present insitu, has a slit which expands or gapes upon loading when the device ispressed together. This gaping may be further pronounced when the patientis e.g. walking whereby the ceiling of the acetabulum is pressed down onthe upper surface of the device and the lower surface of the device ispressed down on the spherical surface of the femoral head.

[0047] Due to the rolling movement (rotation within the joint) of thefemoral head, the possibility exists that the femoral head may pressitself up into the slit of the device during the movement. In suchcases, the press distribution and/or internal movement of the device maybe limited to a minor part of the device that may result in anundesirable increased pressure on that portion of the device. Finally,contact between the femoral head and the acetabulum may occur in casethe femoral head penetrates through the device. However, a devicecomprising parts overlapping each other can prevent this possibleundesirable effect.

[0048] Accordingly, as mentioned above, the device may be curl-shapedwhereby the device with respect to the slit or opening has overlappingparts which do not represent a complete opening in the loadingdirection.

[0049] The size of the prosthetic device according to the invention maybe of any size corresponding to the dimensions of the joint. In a hipjoint, a suitable size is normally one that allows the diameter of thedevice to be about the same or less than the diameter of the femoralhead. However, on some occasions the diameter may exceed that of thefemoral head. The size may also depend on the degree of damage of thenative cartilage of the joint. Moreover, the space available within thejoint in the individual may have an effect on the preferred diameter.Also the compressibility of the material should be taken into account.In the case in which the material is highly compressible, the device mayincrease in diameter upon loading of the joint; when loaded, the deviceshould generally cover the surface area which is covered with cartilagein the normal joint, e.g., in the hip joint, the surface of caputfemoris should preferably be substantially covered when the joint isloaded to avoid contact of the surface of the femoral head with theacetabulum.

[0050] The length of the diameter of the device is designed to fit intothe particular joint, such as between 15-80 mm, such as between 25-70mm, preferable between 30-60 mm, more preferable between 35-50 mm, mostpreferred about 40 mm, when the joint is loaded.

[0051] The prosthetic device according to the invention may vary inthickness depending on the load on the joint, and the thickness of thedevice may also vary within the device.

[0052] The thickness of the device is at least 0.5 mm, such as at least1.0 mm preferably between 2-60 mm, such as between 6-40 mm, preferably8-30 mm, more preferably about 10-20 mm, most preferably about 15 mm inthe unloaded stage. Depending on the material, the device may be highlycompressible, whereby the initial thickness may exceed theabove-mentioned upper limit. If only a limited rotation takes place inthe joint, the thickness of the device may be decreased.

[0053] In one embodiment of the invention, the device is capable oflocking itself to the intra-articular component by at least one elementof the device surrounding the component in such a manner thatdisplacement of the element, and thereby the device, is limited byinterlocking with the component. The intra-articular component which issurrounded is preferably a ligament, such as a ligament nativelyexisting in the joint cavity.

[0054] In one embodiment of the device according to the invention, theelement completely or substantially completely surrounds the ligament.

[0055] Thus, one embodiment of a prosthetic device according to theinvention relates to a device wherein the element interlocking with aligament, when present in situ, permits the ligament to extend throughthe element and substantially exert its natural function on the joint.

[0056] In one aspect of the invention, the prosthetic device is intendedfor the articulation of a hip of a human, said device being adapted suchthat when present in situ in the human hip joint cavity, it comprises atleast one element surrounding ligamentum capitis femoris. Accordingly,ligamentum capitis femoris represents the surrounded intra-articularelement mentioned above.

[0057] It is contemplated that the surrounding of the intra-articularcomponent by the element may be a completely or substantially completelyencircling of the ligament.

[0058] It is also preferred that the prosthetic device, when present insitu, comprises at least one ring-shaped or substantially ring-shapedelement.

[0059] According to another aspect of the invention, the element of theprosthetic device which is adapted to surround the ligament when presentin situ has such a shape and such properties that it can be placedaround the ligament and stay interlocked with the ligament.

[0060] Structural Components

[0061] The device preferably comprises structural components whichpermit arrangement of the body of the device around nativeintra-articular components.

[0062] When the prosthetic device according to the invention is a hipendoprothesis, the device has a shape and structural componentspermitting arrangement of the body of the device around ligamentumcapitis femoris.

[0063] A prosthetic device according to the invention comprises a devicewherein the element of the device interlocking with the device with anintra-articular component has such a shape and/or properties that it iscapable of replacing or supplementing worn or damaged cartilage in thejoint and/or is capable of preventing wear of the native cartilage ofthe joint or of the bone tissue of the joint.

[0064] The structure of the material of the device or of a part of thedevice may be in the form of fibres and filaments which can beincorporated into the matrix in a braided, woven, spongy or spiralpattern, the fibres and filaments having reinforcing properties. Thefibres may be inorganic fibres such as carbide, nitride, boride, carbonand oxide fibres, or the reinforcement may be of organic origin such asDacron™. In a preferred embodiment the fibres are selected frompolyethylene fibres, polypropylene fibres or a combination thereof.

[0065] The structure of the material of the device may comprise alayered or laminated structure, a core of one material or one or moreinterposed layers with different properties enabling an overall functionof the devise suitable for providing a spacer function and/or to exertpressure distribution in the joint when the joint is loaded and/or toprovide at least part of the sliding/rotating movement of the joint byinternal movement of the device, or relevant part of the device.However, it is preferred that the material itself does not compriseinterposed layers resulting in sliding between the layers and therebytear on the mating surfaces within the device. Accordingly, the body ofthe device should be one continuous solid or semi-solid material.

[0066] In one preferred embodiment of the invention, the devicecomprises a tubular passage through which the ligament can pass and besurrounded by the body of the device, as depicted in FIG. 5. Circularmovement around the substantially central ligament is possible butreplacement of the device is prevented. A further feature of thestructure of the device may be that of a slit extending from the outersurface of the device and through the body of the device into thecentral tubular passage. The slit may be curl-shaped in the radialdirection with the axis of the tubular passage being the centre asdepicted in FIGS. 7, 9 and 11.

[0067] The slit may curl or curve into the body of the device so as toform an S-, or C-shaped slit, or zigzag or spiral slit. The curl of theslit may be in the two dimensions of a disc shaped device, as in FIG. 7,or may curl in all three dimensions in the case of a globular,spherical, cone-shaped or cup-shaped device, as depicted in FIG. 9, 19,22, or 27.

[0068] Furthermore, in embodiments where the device comprises more thanone unit, the curvature of the slit may be such as to form a zigzag,spiral or S- or C-shaped multi-unit slit.

[0069] In multi-unit devices, the outer surfaces of the parts of theunit which are in contact with each other may have a surface patternpreventing the units from sliding apart such as grooves or etching orjagged surface pattern, as depicted in FIG. 23.

[0070] Moreover, the overall shape of the device may be from an assemblyof two or more elements of one device, such as two semi-circularelements assembled to form a ring or from the assembly of two elementsobtainable from the cross-sectioning of a ring or globular device alongtheir longest axis. As was the case for the surface of two units, twoelements may have a surface pattern preventing the elements from slidingapart such as grooves or etching or jagged surface pattern. Thus, adevice and its shape may be the result of an assembly of two or moreelements and/or two or more units, each comprising surfaces designed topreventing slippage of units and/or elements, as depicted in FIGS.26-28.

[0071] If suitable, the device may comprise a material which functionsas a frame for the shape or secures the device from opening when placedin situ, for example in the form of a shaped component having theproperties of a spring or the like.

[0072] In one embodiment, the ring-shaped body of the device has a slitor other suitable means which enables the device to be placed in theposition encircling ligamentum capitis femoris.

[0073] Upon loading the device into the joint, the element of the devicesurrounding the component, e.g. a ligament, and thereby interlockingwith the component, may tend to open up due to deformation of the devicein the form of flattening resulting in an increased diameter. When thediameter of the device increases, e.g. the diameter of a ring-shapeddevice comprising a slit, the adjoining surfaces of the slit may gape.

[0074] As stated, during the compression, extension or rotation of thedevice when the device is present in a joint, the slit may have atendency to gape and thus result in reduced weight-bearing effectivenessand/or result in trapping of intra-articular components within the seamof the slit. Preferably, the seam cannot be pulled apart in thedirection of the plane of the seam by the mechanical pressure exerted bythe body of the device conferred by the elastic properties of thematerial.

[0075] To prevent undesired slippage of the seam perpendicular to theplane of the seam, a variety of means may be incorporated into thedesign of the device so as to lock or adhere the two sides of the seam.Preferably, the locking or adherence means are reversible so as to allowremoval or manipulation of the device after initial loading and use.

[0076] The seam is preferably characterised in that a smooth surface isformed in the plane of the seam.

[0077] To prevent the device from opening, the device preferablycomprises overlapping or intersecting parts, such as lips or dovetailsas is known by the person skilled in the art of mechanics or moulding.The two sides of the seam may be adjoined by means of an interlockingdevice such as a protrusion-hole device on sides of the seam.Alternatively, to prevent slippage in perpendicular to the plane of theseam, each side of the seam may be such that each side of the seamcomprises an alternating sequence of angled grooves and correspondingextrusions. Moreover, the top and bottom portion of each side of theseam may comprise alternating teeth and sockets to prevent slippage. Toprevent gaping such overlapping parts and their mating surfaces of thesides of the seam may have an interlocking surface structure. Thepattern of such a structure may include depressions on the matingsurface of one part and corresponding elevations on the other matingpart of the device.

[0078] Accordingly, in one embodiment, the overlapping parts are suchthat the interlocking surface structures constitute grooves. Thesegrooves may extend radially, primarily resulting in a decreased tendencyof the device to “open up” at the area corresponding to the slit or thegap. The grooves may also be orientated in a circulatory structurepreventing the mating surfaces from gliding or sliding apart from eachother. Additionally, the structure may comprise a combination of bothelements reducing undesired movement in both of the two directions, whenthe device is deformed during loading of the joint.

[0079] The terms “radially” and “circular” should be understood asrelative to the centre of the device or relative to the part of thedevice where the ligament extends through the device. “Radially” meaninge.g. grooves being located along radii from the centre, and the term“circular” meaning that e.g. the grooves are located along the peripheryof a circle around the centre.

[0080] In another embodiment, the pattern includes other prominences orknobs, including pointed elevations. Thus, any structure comprising anelevation on one mating surface and a corresponding depression on theother mating surface may result in a decreased movement between themating surfaces. Accordingly, any structure of the mating surfaces whichthereby functions as an interlocking “hook” is within the scope of theinvention. The mating surfaces of the curls may have an interactingprofile in the form of a shape or pattern such as grooved surfaces whichprevent the surfaces from sliding apart by reducing sliding movementsbetween the mating surfaces upon loading of the device.

[0081] Another preferred embodiment of the invention relating to theseam created by the slit in the body of the device, accounts forpreventing of slippage or gaping of the seam by means of a chemicallytreated surface of the sides of the slit. One embodiment of this aspectof the invention anticipates adherence of the two sides of the seam bymeans of photolytically or thermally activating a reaction between thechemically treated surfaces of the sides of the seam once the device hasbeen loaded into the joint. Preferably, this adherence is reversible.

[0082] In another embodiment, the device may also comprise two or moreseparate rings each having a slit which are arranged so that the slitsare orientated in such a way that no direct opening exists in theloading direction, accordingly, the slits are displaced in the directionparallel with the axis of the device. Mating surfaces of such rings mayalso have an interlocking structure as explained above.

[0083] In a still further embodiment, the device is in the form of acurl, wherein the ring-shaped elements together have the overall shapeof a cup. Also in this embodiment, the mating surfaces may comprisegrooves preventing sliding movements of the mating surfaces uponloading.

[0084] In a still further embodiment, the device may comprise minorvertical slits on the outer periphery of the device, these minor slits,e.g., having a depth of 1-5 mm may “absorb” the increasing diameter ofthe device upon loading. Preferably, the part of the device comprisingthe slits (the outer periphery) is not subject to heavy loading whichcould result in particulation of the edges of the device correspondingto the slits. These minor vertical slits on the outer periphery of thedevice may alternatively serve so as to not interfere with movable orimmobile components of the joint within the cavity.

[0085] The device according to the invention may e.g. be processed bymoulding of the material including extrusion and injection moulding.However, any other means for preparing the device of the desired shapecould be utilised.

[0086] In addition, the device may comprise a dye or other materialenabling visualisation of the device such as by X-ray.

[0087] Material Features

[0088] The material features of the device related to features conferredby the chemical composition of the device.

[0089] It is well known in the orthopaedic field to use different typesof materials for prostheses that are suitable for implantation in thebody. The device may be produced from any material or combination ofmaterials suited for implants. However, it is preferable that the bodyof the device does not comprise of any substantial extent of metallicmaterials.

[0090] The combination of materials can be varied according to theproperties preferred for each device. However, the body of the device,is substantially constituted of polymeric material or materials.

[0091] Preferably, the material of which the device is made isbiocompatible, e.g. hemocompatible, thromboresistant, non-toxic, and/ornon-carcinogenic. In addition, the material should be resistant toparticulation, and the solid surface of the material should be so thatthe surface tension is suitable for the interaction between the materialand the biological surfaces.

[0092] Biocompatibility may be assayed through in vitro tests as well asanimal tests. Enzymatic biodegradation may be used as indicative ofbiocompatibility. Furthermore, chondrocytes and fibreblasts may be grownon the material to evaluate the compatibility.

[0093] Finally, biocompatibility may be evaluated by implanting devicesof the material in animals and examining the animal and/or device aftera period of time.

[0094] The device is to be substantially composed of polymeric material,particularly solid or semi-solid polymers. Polymers are the family ofsynthetic or natural macromolecules consisting of inorganic, organicpolymers and combinations thereof. Organic polymers may be natural,synthetic, copolymers, or semisynthetic polymers. Natural polymerscomprise of the class of compounds known as polysaccharides,polypeptides, and hydrocarbons such as rubber and polyisoprene.Synthetic polymers comprise elastomers such as nylon, polyvinyl resin,polyvinyl chloride, polyvinyl dichloride, polyvinylpyrrolidone,polyethylene, polystyrene, polypropylene, polyurethane, fluorocarbonresins, acrylate resins, polyacrylates, polymethylmethacrylate, linearand cross-linked polyethylene, phenolics, polyesters, polyethers,polypyrolidone, polysulfone, polyterpene resin, polytetrafluoroethylene,polythiadiazole, polyvinylalcohol, polyvinylacetal, polyvinyl oxides,and alkyds. Semisynthetic polymers may be selected from cellulosics suchas rayon, methylcellulose, cellulose acetate and modified starches.Polymers may be atactic, stereospecific, stereoregular or stereoblock,linear, cross-linked, block, graft, ladder, high, and/or syndiotactic.The term graft polymer is intended to mean copolymer moleculescomprising a main backbone to which side chains are attached. The mainchain may be a homopolymer or copolymer and the side chains may containdifferent inorganic or organic constituents.

[0095] The device may comprise of cross-linked polymers elastomers suchas high consistency elastomers, rubber, elastin and collagen. Thematerial may be selected from polyurethane, elastin, collagen andcombination products thereof. Alternative embodiments of materialssuitable for the surface of a device according to the invention include,in addition to the materials mentioned supra and infra includehyaluronic acids and derivatives thereof.

[0096] Preferred polymeric materials are however presently believed tobe those selected from the group comprising polyolefins, such aspolyethylene, polypropylene, polybutene, polyisoprene, andpolyvinylpyrrolidone, combinations thereof, their copolymers, andgrafted polymers thereof, particularly polyethylene and polypropylene,most particularly polypropylene.

[0097] Polymers and copolymers of polypropylene or polyethylene, as wellas grafted forms of each of these are particularly interesting.Moreover, surface treated forms of these polymers, copolymers or graftedpolymers are of notable interest.

[0098] The structure of the material of the device or of a part of thedevice may be in the form of fibres and filaments which can beincorporated into the matrix in a braided, woven, spongy or spiralpattern, the fibres and filaments having reinforcing properties. Thefibres may be inorganic fibres such as carbide, nitride, boride, carbonand oxide fibres, or the reinforcement may be of organic origin such asDacron™. In a preferred embodiment the fibres are selected frompolyethylene fibres, polypropylene fibres or a combination thereof. Thefibres may be surface treated before incorporated into the matrix toobtain a better adhesion of fibres to matrix.

[0099] The present invention in particular relates to a device composedof material formulations intended to meet the specifications ofdurability, biocompatibility, etc. These properties are obtainable bytreating polymer materials, such as polyethylene, polypropylene orpolyvinylpyrrolidone or combinations and co-polymers thereof as well asprecursor materials for polymerisation, with high-energy electrons,gamma rays, photons, microwaves, ion implantation, plasma treatment,annealing, thermal radiation or another radiation to obtain idealdurability and biocompatibility of the new, modified material. Treatmentof the above-mentioned materials with radiation leads to cross-linkingof polymers and thereby generating new, modified materials. Preferably,the polymer material is a cross-linked polypropylene material. Inanother embodiment the polymer material is a cross-linked polyethylenematerial.

[0100] A device according to the invention preferably comprises at leasta first polymeric component and a second polymeric component, whereinthe chain length of the first polymeric component is longer than thechain length of the second polymeric component. The first polymericcomponent is providing the physical properties, such as strength of thedevice as discussed below. Due to the longer chain length the strength,in particular the tensile strength, of the device is increased. Thechain length of the first polymeric component is preferably above 100monomer units, such as above 120 monomer units, preferably above 150monomer units. The chain length of the second polymer is preferably atmost 99% of the chain length of the first polymer, such as at most 95%,such as at most 90%, such as at most 80%, such as at most 70%, such asat most 60%, such as at most 50%.

[0101] In one embodiment the device comprises a body constituted by thefirst and the second polymeric components. The body may optionally betreated in order to optimise the properties such as surface properties,biocompatibility and/or low friction. By the term “body of the device”is meant the part of the device providing the strength properties aswell as the resiliency properties.

[0102] In another embodiment the device comprises a body constituted bythe first polymeric component, whereas the second polymeric componentprovides optimised surface properties.

[0103] In a preferred embodiment the first polymeric component isselected from polymers having a carbon-backbone.

[0104] The first polymeric component may be selected from polyacrylates,polystyrene, polyethers, polytetrafluorethylene, polyvinylalcohol,polyethylene, and polypropylene.

[0105] When the body is constituted by two components, the secondpolymeric component may be selected from polyacrylates, polystyrene,polyethers, polytetrafluorethylene, polyvinylalcohol, polyethylene, andpolypropylene. Preferred combinations for the first and the secondpolymeric component are polyethylene and polypropylene, polyethylene andpolyethylene, or polypropylene and polypropylene, in the latter twocases, the first and the second polymeric components is comprised ofidentical monomers, whereas the polymers thereof are of different chainlength. When the monomers of the two polymeric components are identicalthe prosthetic device is preferably compounded to form a bidispergentsystem.

[0106] The second polymeric may in a preferred embodiment be across-linked polymer. The combination of a polymer having a high chainlength and a polymer having a shorter chain length, but beingcross-linked provides a strong device yet having the resilientproperties necessary for the device.

[0107] Furthermore, radiation also allows grafting of polymers ontoexisting polymer surfaces, resulting in new mechanical properties aswell as new surface properties. In this manner, the resulting modifiedpolymer device can be processed to meet the necessary requirements ofdurability and biocompatibility.

[0108] Polymers may be prepared by methods known to the person skilledin the art. Chemical catalysis, thermal induction or photo induction areanecdotal non-limiting examples of methods of preparing the polymers.The cross-linking of the polymers or grafting may be done by radiationor other methods known to the person skilled in the art.

[0109] The properties of the materials to be obtained by thesecross-linking and grafting processes are preferably i) resistance totear and wear; ii) good compressibility; iii) flexibility and surfaceproperties which will allow wetting with biological fluids, and/oreventually allow growth of chondritic cells onto the prosthetic device.

[0110] Typically, the device is prepared by a process comprising of thefollowing steps:

[0111] The prosthetic devise is formed by casting the pure polymer or ablend of polymers in a mould of specified dimensions. The polymer ischosen from the above mentioned polymers.

[0112] After hardening the cast material as formed, or after swelling ina suitable solvent, the device is subjected to high-energy electrons,gamma rays or another radiation in order to create cross-linking whichwill modify the mechanical properties of the cast material to meet thepreferred specifications.

[0113] Finally, eventually after removal of the swelling solvent, thesurface of the cast material is treated to achieve good surfaceproperties as described above.

[0114] The surface of the device can subsequently be treated to modifysurface properties such as wetting ability and/or biocompatibility. Thissurface treatment can be performed by plasma treatment, chemicalgrafting or by a combination of plasma treatment and chemical grafting.The surface of the device contacting with the articulating surfaces ofthe joint may be of such a material which forms a uniform contactsurface reducing the overall contact stress per unit area, and therebyavoiding corrosion of the articulating surfaces of the joint.Accordingly, the material contacting with the biological surfaces may besmooth, biocompatible, preferably self-lubricating, and it should bewear-resistant so that powder generated due to wear is avoided in thatthis could otherwise result in foreign matter reactions and causefurther trouble to the function of the joint.

[0115] Furthermore, the surface material should preferably be a materialor a combination of materials having self-repairing properties so thatfissures, cracks or other ruptures on the surface do not exceeduncontrollable levels. However, the surface material is preferablycontinuous with the material of the rest of the device, e.g. thematerial may gradually merge into the material of the inner core ormatrix of the device.

[0116] The surface of the material may be chemically treated so as tosoften, rigidify or lubricate the surface of the device or partsthereof. The surface of the material may be coated so that the coatingconfers these properties, or may be treated so as to chemically alterthe surface of the device so as to confer any of these properties.Alternatively, certain polymer surfaces may be modified by means ofthermal or photolytic energy.

[0117] Also the surface treatment may be provided by incorporatingsurface treatment polymer, such as polyvinyl pyrrolidone, into thematrix to maintain the good surface properties.

[0118] Independent of whether-the body of the device comprises one ortwo components, it is preferred that the body of the device is providedwith a treatment resulting in a functional surface of the device beingwettable by the joint fluid normally present in the joint cavity, inoder to decrease any friction between the device and joint parts, suchas bone, cartilage, ligaments and mucosa.

[0119] Without being bound by theory it is also believed that a wettedsurface reduces the risk of having the immune system recognising thedevice when implanted, which would otherwise lead to adverse effects ofthe device.

[0120] By the term “functional surface” is meant the external surface ofthe device, ie. the surface contacting joint cavity parts. Since thebody of the device is often produced as one, two or even threedimensional networks, internal surface may be present in the body, saidinternal surfaces often corresponding with the external surfaces.

[0121] Thus, the prosthetic device preferably comprises a thirdpolymeric component, said third polymeric component being different fromthe first and/or the second polymeric component. The third componentwill preferably be grafted to the body of the device and result in theimproved surface properties. The third polymeric component is preferablyselected from polyethylene oxides, and polyvinylpyrrolidon, mostpreferably from polyvinylpyrrolidon.

[0122] When the body is comprised of one component, such as wherein thefirst polymeric component comprises a copolymer of polyethylene andpolypropylene or wherein the first polymeric component is a cross-linkedpolymer, the second polymer may be grafted to the first polymer and actas the third polymeric component as described above.

[0123] Preferred devices are composed of:

[0124] A body of polyethylene having polyvinylpyrrolidone graftedthereto

[0125] A body of two polyethylene polymers of different chain lengthshaving polyvinylpyrrolidone grafted thereto

[0126] A body of polypropylene having polyvinylpyrrolidone graftedthereto

[0127] A body of two polypropylene polymers of different chain lengthshaving polyvinylpyrrolidone grafted thereto

[0128] A body of a copolymer of polyethylene and propylene havingpolyvinylpyrrolidone grafted thereto

[0129] A body of a polyethylene and a copolymer of polyethylene andpolypropylene having polyvinylpyrrolidone grafted thereto

[0130] A body of polypropylene and a copolymer of polypropylene andpolyethylene having polyvinylpyrrolidone grafted thereto

[0131] A body of polyethylene having 2-vinylpyrrolidone grafted thereto

[0132] A body of two polyethylene polymers of different chain lengthshaving 2-vinylpyrrolidone grafted thereto

[0133] A body of polypropylene having 2-vinylpyrrolidone grafted thereto

[0134] A body of two polypropylene polymers of different chain lengthshaving 2-vinylpyrrolidone grafted thereto

[0135] A body of a copolymer of polyethylene and propylene having2-vinylpyrrolidone grafted thereto

[0136] A body of a polyethylene and a copolymer of polyethylene andpolypropylene having 2-vinylpyrrolidone grafted thereto

[0137] A body of polypropylene and a copolymer of polypropylene andpolyethylene having 2-vinylpyrrolidone grafted thereto

[0138] Mechanical Features

[0139] The mechanical features of the device relate to propertiesconferred by the structural and/or material features of the device.

[0140] The present invention provides new material formulations intendedto meet the specifications of a durable, biocompatible device. Thepresent device may be produced from materials hitherto unknown forimplants as long as the following material features and requirements aremet and that the materials have optimised properties relating to:

[0141] Mechanical, chemical and physical stability and optimisedtribological properties.

[0142] Good biocompatibility.

[0143] Resistance to elevated temperature (sterilisation).

[0144] Affinity to the surrounding biological components.

[0145] Dynamic characteristics suitable for stress distribution.

[0146] Furthermore, as stated supra, radiation allows grafting ofpolymers onto existing polymer surfaces, resulting in new mechanicalproperties as well as new surface properties. In this manner, theresulting modified polymer device can be processed to meet the necessaryrequirements of durability and biocompatibility.

[0147] The surface of the device can subsequently be treated to modifysurface properties such as wetting ability and/or biocompatibility. Thissurface treatment can be performed by plasma treatment, chemicalgrafting or by a combination of plasma treatment and chemical grafting.

[0148] The properties of the new materials to be obtained by thesecross-linking and grafting processes are: resistance to tear and wear,good compressibility and flexibility and surface properties which willallow wetting with biological fluids, and/or eventually allow growth ofchondritic cells onto the prosthetic device.

[0149] It is believed that the surfaces of the device in contact withbiological surfaces within the joint will be subject to interactionsresulting from frictional resistance, since only part of thesliding/rotating movement of the joint will take place by internalmovement of the device.

[0150] The surface material should also be elastic in order to allowdeformation of the shape without damage to the continuity of the surfacebut should on the other hand also secure stability of the overall shapeof the device.

[0151] The inner matrix of the device should be suitable for stressdistribution such as materials being pressure absorbent, havingelongation properties and rigidity. Preferably, the device is composedof a single homogenous material or a combination of materials having thesurface properties mentioned above as well as the relevant dynamiccharacteristics suitable for stress distribution. Preferably, the devicecomprises exclusively of solid or semi-solid non-metallic material.

[0152] Mechanical properties for certain relevant polymers are describedby Szycher (Szycher, M. (editor), sponsored by SPE, Society of PlasticsEngineers, Inc. Biocompatible Polymers, Metals, and Composites, pp.725-727, 757-61).

[0153] Mechanical properties of polymers are controlled by the elasticparameters, the three moduli: elastic, shear, and compressive moduli.These parameters are theoretically interrelated. A modulus is the ratiobetween the applied stress and the corresponding deformation. Thereciprocals of the moduli are called compliancies. The three elasticmoduli have the dimension: force per unit area, (N/m² or Pa). Polymersare not normally ideal elastic bodies, but under load they show (timedependant) viscoelastic properties. By taking the load intoconsideration, the properties should be viewed according to thisdilemma. Also, ideal elastic properties and ultimate properties, areinfluenced by the viscoelastic properties.

[0154] Ultimate tensile strength is a measure of the stress required tocause the material to rupture in tension. Ultimate elongation is thepercent stretch of the material before it ruptures in tension.Elongation (%) is measured as${{Elongation}\quad ({percent})} = {\frac{S_{B} - S_{o}}{S_{o}} \times 100}$

[0155] where S_(B)=observed distance between bench marks of thestretched specimen at rupture, and S_(o)=the original distance betweenbench marks. TABLE 1 Elastic parameters and their definitions Elementarymode of deformation Elastic parameter Symbol Isotropic (hydrostatic)Bulk modulus K compression bulk compliance or κ compressibility (κ =1/K) Simple shear Shear modulus or rigidity G Shear compliance J (J =1/G) Uniaxial extension Tensile modulus or E Young's modulus Tensilecompliance S (S = 1/E) Any Poisson ratio ν Symbol Definition K$\frac{{Hydrostatic}\quad {Pressure}}{{Volume}\quad {change}\quad {per}\quad {unit}\quad {volume}} = {\frac{p}{{\Delta V}/V_{0}} = \frac{{pV}_{0}}{\Delta V}}$

κ (κ = 1/K) reciprocal of foregoing G$\frac{{Shear}\quad {force}\quad {per}\quad {unit}\quad {area}}{\begin{matrix}{{Shear}\quad {per}\quad {unit}\quad {distance}} \\{{between}\quad {shearing}\quad {surfaces}}\end{matrix}\quad} = {\frac{F/A}{\tan \quad \gamma} = {\frac{\tau}{\tan \quad \gamma} \approx \frac{\tau}{\gamma}}}$

J (J = 1/G) reciprocal of foregoing E $\frac{\begin{matrix}{{Force}\quad {per}\quad {unit}} \\{{cross}\text{-}{sectional}\quad {area}}\end{matrix}}{{Strain}\quad {per}\quad {length}} = {\frac{F/A}{\ln \left( {L/L_{0}} \right)} = {\frac{\sigma}{ɛ} = \frac{F/A}{{\Delta L}/L_{0}}}}$

S (S = 1/E) reciprocal of foregoing (strain/stress) ν$\frac{{Change}\quad {in}\quad {width}\quad {per}\quad {unit}\quad {width}}{{Change}\quad {in}\quad {length}\quad {per}\quad {unit}\quad {length}} = \frac{{lateral}\quad {contraction}}{{axis}\quad {strain}}$

[0156] Examples of ranges of the mechanical properties of the device arementioned below. However, it should be contemplated that not all of thefollowing characteristics may be fulfilled by the material of theprosthetic device since, as explained above, the numerous properties ofthe material are theoretically interrelated. Accordingly, conflict infulfilling all parameters within the stated ranges may occur.

[0157] In one embodiment, the prosthetic device according to theinvention is a device wherein the material of the device or at least thepart of the device which exerts the pressure distribution and/or thepart which exerts the sliding/rotating movement in the joint when thejoint is loaded has/have one or more of the following properties (underbiological conditions (37° C., physiological salinity)): A compressivemodulus (K) of at least 2000 MPa, a shear modulus (G) of at least 1 MPaand an elastic module (E) of at least 10 MPa.

[0158] Furthermore, certain requirements to the material under stresswith forces that ultimately leads to disintegration can be expressed.Based on the elasticity parameters for the material, the properties ofthe material with respect to pressure, elongation, torsion anddisplacement in the range where the material responds elastic can beestimated. The ultimate limits should preferably be within ±20% of therange of elastic response. As a consequence thereof, the limits for theultimate properties (ultimate compression strength, tensile strength,torsional strength, shearing strength) can be derived.

[0159] Furthermore, the material should have an “ultimate percentageelongation” of at least 20%.

[0160] The materials according to the invention may be a “quasi elastic”material. Y. Shikinami and H. Kawarada, Biomaterials 19, 1998, pp.617-635, discuss that many materials of biological origin, has a J-formin a stress vs strain curve, whereas may synthetic materials has anS-form.

[0161] Preferably, the critical surface tension (γ_(c)) values should bewithin the “zone of biocompatibility” corresponding to the range ofabout 20-30 dynes/cm (as defined by Lelah M. D., Cooper, S. L.,Polyurethanes in Medicine—CRC Press, Inc. Boca Raton, Fla., pp. 59-62and 92-93).

[0162] In one embodiment of combined features, the diameter of thedevice is about 35 mm and the thickness is about 5 mm and the materialof at least a part of the device has an ultimate percentage elongationof at least 20% corresponding to an ultimate angle of twist of about90°.

[0163] In another such embodiment, the diameter of the device is about35 mm and the thickness is about 10 mm and the material of at least apart of the device has an ultimate percentage elongation of at least 20%corresponding to an ultimate angle of twist of about 90°.

[0164] In a further embodiment, the diameter of the device is about 35mm and the thickness is about 10 mm and the material of at least part ofthe device has an ultimate percentage elongation of at least 20%corresponding to an ultimate angle of twist of about 180°.

[0165] Insertion

[0166] It is also an object of the present invention to provide a methodfor introducing a device according to the present invention into ajoint. The method comprises:

[0167] a) locking the device to an intra-articular component and therebyfixing or retaining the device in the joint cavity in a manner which issubstantially non-invasive with respect to cartilage and bone nativelypresent in the joint cavity.

[0168] The method may further comprise any of the following steps beforelocking the device to the intra-articular component in the joint:

[0169] i) exposing the joint capsule by conventional surgery procedures,

[0170] ii) penetrating the joint capsule into the joint space leaving apassage for

[0171] iii) introducing the prosthesis into the joint capsule via thepassage, the prosthesis having a shape suitable for being introducedthrough this passage.

[0172] Locking the device to the intra-articular component and therebyfixing or retaining the device in the joint cavity in a manner which issubstantially non-invasive with respect to cartilage and bone nativelypresent in the joint cavity may include encircling a ligament present inthe joint with a ring-shaped element of the device such as a ring-shapeddevice having a slit extending from the periphery of the device to thecentral opening of the “ring”.

[0173] The method may further comprise the steps of deforming theprosthetic device into a reduced volume or a slender shape beforelocking the device to the intra-articular component.

[0174] In the case of insertion into a hip joint, the insertion of thedevice is preferably performed after penetration through the head of therectus femoris muscle leaving a passage having a substantial width forintroducing means into the joint capsule without alteration of thefunction of the capsule after the surgery.

[0175] Means or instruments for inserting the device into the jointspace can be in the form of forceps comprising means for deforming thedevice into a minor volume or a more slender shape and may comprisemeans for grasping around the intra-articular component to which thedevice is capable of interlocking.

[0176] The forceps may further comprise means for locking the devicearound or substantially around the intra-articular component andoptionally means enabling the forceps to be withdrawn withoutwithdrawing the device.

[0177] Thus, a further object of the invention relates to a kitcomprising:

[0178] a) an intra-articular prosthetic device for a joint having

[0179] a.1) a spacer function and/or capability to exert pressuredistribution and/or sliding/rotating movement of the joint by aninternal movement of the device by means of a resilient member, and

[0180] a.2) a locking mechanism adapted to fix the device to anintra-articular component by means of an element of the devicesurrounding the component in such a manner that displacement of thedevice is limited by inter-locking with the component; and

[0181] b) an instrument for inserting the prosthetic device into a jointcavity

[0182] Preferably, the elements of the kit should be sterile.

[0183] The instrument b) may further comprise one or more of thefollowing means b.1 to b.4:

[0184] b.1) means for deforming the prosthetic device into a reducedvolume or to a slender shape and keeping this volume or shape uponintroduction of the device to the joint;

[0185] b.2.) means for grasping or encircling the intra-articularcomponent to which the element of the prosthetic device is capable ofinter-locking;

[0186] b.3.) means for leaving the prosthetic device in the joint withthe element of the prosthetic device surrounding an intra-articularcomponent; and

[0187] b.4.) means for retracting the instrument from the joint.

[0188] It is contemplated that each of the means of b.1.), b.2.), b.3.)and b.4.) may be connected to or form part of a handle. Moreover, theresilient member of a.1) and the element surrounding the intra-articularcomponent of a.2) may constitute the prosthetic device.

[0189] The means of b.2.) for grasping or encircling the intra-articularcomponent may comprise an incision of the instrument which, in situ, isable to substantially retain the element within the “legs” of theincision.

[0190] Biological Activity of the Device

[0191] When inserted in the joint cavity the device is capable ofalleviating the pain and other symptoms related to damaged cartilage,such as improving movements. Furthermore, the device may be capable ofhealing the sick bone's structure and/or cartilage structure—in hole ofpartly.

[0192] For example the device may facilitate creation of new cartilageand/or minimise destruction, such as fibrillation and/or fragmentation,of cartilage by relieving the pressure on the residual cartilage/bone inthe joint

[0193] Furthermore, the device may comprise biological active additives.Medication or biological active substances can be used as additive tothe device to facilitate healing, minimise destruction or with othertherapeutic goals, such as pain relieve, anti-inflammation, oncologytreatments, stimulation of bone growth, and/or anti-infectious agents.Also, biological osteogenic or chondrogenic, chondral inductive, and/orchondral conductive materials may be added to the device. In particularpatients suffering from osteoporosis or other bone degeneratingconditions may benefit from having devices comprising osteogenicinductive materials implanted.

[0194] The medication or biological active substances can be used asadditive to the device to facilitate cell growth, such as osteocytes,osteoblasts, chondrocytes, chondroblasts, mesenchymal cells. Cartilageinducing factor may for example be the factors described in U.S. Pat.No. 4,774,322 and U.S. Pat. No. 4,843,063

[0195] The device itself can be used as a growth medium and/or networkfor the natural or artificial cells, such as chondrocytes.

[0196] The device is capable of being formed to suit any joint cavity ofanimals or human beings, therefore the device may for example be formedto fit into any one of the following joints: Hip joint, knee joint,ankle joints, shoulder joint, elbow joints, wrist, fingers, spinalcolumn joints, such as for substituting intervertebral discs, and thejaw joint.

BRIEF DESCRIPTION OF THE DRAWINGS

[0197]FIG. 1 shows a cross sectional perspective view of a human hipjoint.

[0198]FIG. 2 shows a cross sectional perspective view of the hip bonecorresponding to FIG. 1.

[0199]FIG. 3 shows a cross sectional perspective view of the human hipbone in which one embodiment of a device 11 according to the inventionis shown in situ.

[0200]FIG. 4 shows a perspective view of the human hip joint in whichthe femoral head has been retracted from the acetabulum.

[0201]FIG. 5 shows a perspective view in which one embodiment of adevice 11 according to the invention is located in situ.

[0202]FIG. 6 shows a cross sectional perspective view of an embodimentof the device according to the invention disclosing a device having aglobular shape.

[0203]FIG. 7 shows an elevational perspective view of a sphericallyshaped device.

[0204]FIG. 8 shows a cross sectional perspective view of a cup-shapeddevice.

[0205]FIG. 9 shows a perspective view of a cup-shaped device accordingto the device shown in FIG. 8.

[0206]FIG. 10 shows a cross sectional perspective view of anotherembodiment of a cup-shaped device.

[0207]FIG. 11 shows an elevational perspective view of the embodiment ofa device as shown in FIG. 10.

[0208]FIG. 12 shows a cross sectional perspective view of a ring-shapeddevice.

[0209]FIG. 13 shows an elevational perspective view of a ring-shapeddevice.

[0210]FIG. 14 shows a cross sectional perspective view of asubstantially disc-shaped embodiment of the device.

[0211]FIG. 15 shows a cross sectional perspective view of a ring-formedembodiment of the device consisting of a substantially homogeneousmaterial.

[0212]FIG. 16 shows a cross sectional perspective view of a doublering-shaped embodiment of the device.

[0213]FIG. 17 shows a perspective view of an embodiment of a devicecomprising two ring-shaped elements.

[0214]FIG. 18 shows a cross sectional perspective view of an embodimentof the device in showing vertical lines corresponding to grooves on thesurfaces representing a slit.

[0215]FIG. 19 shows an elevational perspective view of an embodiment ofthe device corresponding to the one shown in FIG. 18.

[0216]FIG. 20 shows a cross sectional perspective view of a devicesubstantially similar to the one shown in FIG. 17.

[0217]FIG. 21 shows an elevational perspective view comprising a doublering having slits of the upper part and the lower part (the rings).

[0218]FIG. 22 shows a cross sectional perspective view of a curl-shapedembodiment of the device.

[0219]FIG. 23 shows a sectional perspective view of an embodiment of thedevice comprising curl-shaped element or a double ring.

[0220]FIG. 24 shows a cross sectional perspective view of a ring-formedembodiment.

[0221]FIG. 25 shows a cross sectional perspective view of a ring-shapedelement in which the hole or passage of the ring is placedeccentrically.

[0222]FIG. 26 shows a cross sectional perspective view of an embodimentof the device corresponding to the one seen in FIG. 16.

[0223]FIG. 27 shows a perspective view of an embodiment similar to theone shown in FIG. 26.

[0224]FIG. 28 shows a cross sectional perspective view of a ring-shapedelement, e.g. corresponding to the lower part of the ring-shaped elementseen in FIG. 27.

[0225]FIG. 29 shows a perspective view of one embodiment of aninstrument with the prosthetic device located between the upper part ofthe instrument facing the surface corresponding to the acetabulum insitu and the lower part facing the femoral head.

[0226]FIG. 30 shows a perspective view of the upper part of theinstrument as shown in FIG. 29.

[0227]FIG. 31 shows a sectional perspective view of an embodiment of theupper part of the instrument comprising an edge or wall of a V-shapedincision.

[0228]FIG. 32 shows a perspective view of the embodiment shown in FIG.31 but seen from above.

[0229]FIG. 33 shows a perspective view of an embodiment of the upperpart of the instrument comprising pushing means and means for securingthe prosthetic device.

[0230]FIG. 34 shows a perspective view of a scissors-like embodiment ofan instrument suitable or insertion of the device into the joint.

[0231]FIG. 35 shows a perspective elevational view of a hip jointwherein the femoral head has been retracted from the acetabulum givingspace for the insertion of the device by use of an embodiment of theinstrument according to the invention.

[0232]FIG. 36 shows a view similar to the one is FIG. 35 in which theinsertion of the device is taken place. The upper and lower part of theinstrument now gradually opened for delivering the device into the jointand to place the device around the ligament.

EXAMPLES A Procedure for Producing a Device According to the InventionExample 1

[0233] The device is produced using compression molding. A preformedfibre network consisting of polyethylene fibres (Dyneema®, DSM Holland)wetted with a plastomer of the polyethylene type (Hostalen®, DSMHolland) is heated and compressed into the shape of the finished devicein an appropriate mold. The heating procedure ensures that the plastomerflows together. The heating temperature is selected below the meltingtemperature of the fibre crystallites in order not to loose thecrystallinity of the polyethylene fibres, ie. below 140° C., and abovethe melting temperature of the polyethylene plastomer, ie. in the rangebetween 100-140° C. Subsequent cross-linking of both fibres andplastomer is obtained using treatment with accelerated electronsfollowed by annealing. As the cross-linking process takes place in theamorphous polyethylene regions, the optimal dose will depend on thefraction of amorphous polyethylene in the final device. The optimalradiation dose is close to the gelation dose of polyethylene and thuslie between 30 and 300 kGy (3-30 Mrad). The purpose of annealing is toeliminate long living free radicals by a heat treatment of 80° C. forabout 12 hours in vacuum. Subsequent surface grafting withpolyvinylpyrrolidone is obtained by irradiating the device surrounded bya solution of polyvinylpyrrolidone, wherein the irradiation dose is inthe range between 10 and 100 kGy. After the grafting procedure thedevice is washed with water to remove ungrafted polyvinylpyrrolidone.

Example 2

[0234] The device is produced as described in Example 1, except thatpolyvinylpyrrolidone is substituted with a solution of2-vinylpyrrolidone.

Example 3

[0235] The device is produced as described in Example 1, except thatpolyvinylpyrrolidone is substituted with a solution of a combination ofpolyvinylpyrrolidone and 2-vinylpyrrolidone.

A Surgical Procedure for Insertion of a Prosthetic Device According tothe Invention into the Hip Joint

[0236] Antero-lateral exposure of hip. Modified Smith-Petersen approach(Smith-Petersen M. N.; Approach to and exposure of the hip joint formold arthroplasty. J. Bone Joint Surgery 1949; 31 A: 40)

[0237] Technique: Position of patient: The patient may lie supine on theoperation table. Traction may be applied by use of bone traction in thefemoral condyles, or by soft tissue traction in a boot as used whenosteosynthezising a proximal femoral hip fracture. A counter extensionmay be applied by an external pin placed on the symphysis. A smallsandbag may be placed under the buttock of the affected side to rotatethe trochanter slightly forwards. Some may prefer the postero-lateralapproach with the patient in the lateral position, but the approach maybe more difficult with respect to reaching the teres ligament in the hipjoint.

[0238] Incision: The incision forms an angle open anteriorly. Its upperlimb begins 4 cm behind the anterior superior spine of the ileum andextends obliquely backwards to the tip of the greater trochanter. Thelower limb of the incision extends vertically downwards from the greatertrochanter for 5 cm. The skin flaps are mobilised from the underlyingdeep fascia, which is cleared of adherent adipose tissue.

[0239] The deep exposure: When the deep fascia has been incised, theinterval between the tensor fascia latae muscle anteriorly and thegluteus medius posteriorly is identified immediately proximal to theantero-superior corner of the greater trochanter. This interval iswidened by separating the fibres with dissecting scissors and iscontinued proximally. Towards the crest of the ileum, the two musclesare blended more closely and have to be separated by sharp dissectionwith scissors. The space between the muscles is opened up by strippingpart of the muscle origins from the outer aspect of the wing of ileum.Closer to the trochanter, the gluteus minimus may also be partly raisedfrom the bone and retracted posteriorly. In the lower half of the wound,the capsule of the hip joint now comes into view with, immediately aboveit, the reflected head of the rectus femoris muscle. The reflected headand the anterior part of the capsule is to be preserved and is opened byan H-shaped incision and flaps turned proximally and distally.

[0240] The maximal traction is now performed. A space in the joint of1.5 cm is needed. Relevant elongation of muscles and tendons may beperformed. Adduction tenotomy may be performed by a small stab woundincision, whereas the rectus can be reached by the antero-lateralapproach.

[0241] The grab-forceps with the hip joint device is now inserted, andthe retractor may help to catch the teres ligament of the head of femur.

[0242] The hip joint must be tested to verify the stability of the hipjoint device. The hip ring is allowed to space the relaxed joint by0.8-1.5 cm.

[0243] The capsule is closed with two or three Vicryl sutures, afterwhich the separated muscles are likewise approximated with interruptedsutures. The skin is closed with deep tension sutures and skin edgesutures. A suction drainage may be used according to the circumstances.

DETAILED DESCRIPTION OF THE DRAWINGS

[0244]FIG. 1 shows a cross sectional perspective view of a human hipjoint where the femoral head 1 is shown in connection with the femoralneck (collum femoris) by the joint cavity 3 (cavum articulare). Thejoint cavity 3 is separated from the outside by the joint capsule 4(capsula articulare). From the femoral head 1, ligamentum femoris 5extends through the joint cavity 3 between the acetabulum 6 and thecartilage 7 covering the femoral head 1. Ligamentum femoris 5 isanchored in the bone of the femoral head at one end and the ligamentfibres are attached to the acetabulum 8 which is part of the hip bone 6(os coxae).

[0245]FIG. 2 shows a cross sectional perspective view of the hip bonecorresponding to FIG. 1. However, e.g. due to damage of the femoralhead, the cartilage is missing and the bone of the femoral head is indirect contact with the acetabulum. Both the surface of the acetabulumand the surface 9 of the femoral head 1 are damaged. The intactligamentum femoris 5 extends through the joint cavity 3.

[0246]FIG. 3 shows a cross sectional perspective view of the human hipbone in which one embodiment of a device 11 according to the inventionis shown in situ. Ligamentum femoris 5 extends from its attachment ofthe femoral head through the device and is located between theacetabulum and the upper surface of the device.

[0247]FIG. 4 shows a perspective view of the human hip joint in whichthe femoral head 1 has been retracted from the acetabulum 8. Ligamentumfemoris 5 is anchored in the femoral head at one end the other end islocated in the acetabulum 8 of the hip bone 6.

[0248]FIG. 5 shows a perspective view in which one embodiment of adevice 11 according to the invention is located in situ covering thefemoral head and surrounding ligamentum femoris 5 which thereby extendsthrough the device 11. When the ligament is surrounded by the device,replacement of the device is prevented. However, circular movementaround the substantially central ligament is possible.

[0249]FIG. 6 shows a cross sectional perspective view of an embodimentof the device according to the invention disclosing a device having aglobular shape in which a tubular passage 30 extends through the device31. The passage extends along the central axis from one pole to theopposite pole.

[0250]FIG. 7 shows an elevational perspective view of a sphericallyshaped device having a central tubular passage 30 extending through thedevice 33 and a slit 32 extending from the outer surface of the deviceand through the body of the device into the central passage 30. The slitmay be curl-formed in the radial direction with the axis of the tubularpassage being the center.

[0251]FIG. 8 shows a cross sectional perspective view of a cup-shapeddevice having a central passage 34 extending from the convex upper partto the flattened bottom of the device 35.

[0252]FIG. 9 shows a perspective view of a cup-shaped device accordingto the device shown in FIG. 8. The device 37 has a slit 36 extendingfrom the surface of the device into the central passage 34 shown as ahole of the upper part of the device.

[0253]FIG. 10 shows a cross sectional perspective view of anotherembodiment of a cup-shaped device 39 having an upper convex surface anda lower surface 40 which is concave and forms a half spherical cavityhaving a passage 38 which extends to the upper convex surface of thedevice.

[0254]FIG. 11 shows an elevational perspective view of the embodiment ofa device as shown in FIG. 10. The slit 41 has a substantially S-shapedcourse which extends through the device 42 from the centre to theperiphery of the device.

[0255]FIG. 12 shows a cross sectional perspective view of a ring-shapeddevice. The central part 44 is composed of a reinforced materialcompared to the rest of the device material 45. The central surface 43represents the part of the device in contact with the ligament.

[0256]FIG. 13 shows an elevational perspective view of a ring-shapeddevice in which the slit 46 has a substantially tongued course. Such atongued course of the slit may represent overlapping parts in a planesubstantially perpendicular to an axis through the central passage ofthe device. As appears from the figure, the slit 46 extends from thecentral hole to the outer periphery 47 of the device.

[0257]FIG. 14 shows a cross sectional perspective view of asubstantially disc-shaped embodiment of the device showing the centralpassage 48 extending from the outer surface 49 through the device. Apart of the central material 51 is shown as reinforced compared to therest of the material 50 of the device.

[0258]FIG. 15 shows a cross sectional perspective view of a ring-formedembodiment of the device consisting of a substantially homogeneousmaterial 52. As shown, the periphery of the device, where the upper andlower surface meet, is less rounded compared to the correspondingcentral part 53.

[0259]FIG. 16 shows a cross sectional perspective view of a doublering-shaped embodiment of the device (a device consisting of two units)having the overall shape of a cup comprising a cavity corresponding tothe lower surface which is in contact with the femoral head. The upperring 54 being smaller than the lower ring 55. The device may compriserings of different materials.

[0260]FIG. 17 shows a perspective view of an embodiment of a devicecomprising two ring-shaped elements. The upper ring 57 of the device maycontinue in the lower ring 58 around the axis of the central hole 56.Accordingly, the device, having a slit which has the course between thesurfaces of the upper and the lower rings, can be arranged around theligament by a rotating movement until the ligament is positioned in thecentre of such curly device.

[0261]FIG. 18 shows a cross sectional perspective view of an embodimentof the device in which the vertical lines 70 represent top and bottom,respectively, of grooves forming a zigzag-shaped slit extending in theradial direction from the central hole to the periphery as well as fromthe upper to the lower surface of the device.

[0262]FIG. 19 shows an elevational perspective view of an embodiment ofthe device corresponding to the one shown in FIG. 18. The zigzag-shapedslit 71 has a substantially radial direction.

[0263]FIG. 20 shows a cross sectional perspective view of a devicesubstantially similar to the one shown i FIG. 17 in which the tworing-shaped elements 72 and 73 of the curl together form an upperspherical surface fitting into the acetabulum and comprising a lowercavity which is also of a spherical shape which fits on the femoralhead. The upper ring-shaped element 72 comprises a central passage forthe ligament which is thereby surrounded by the upper ring. The contactzone 74 constitutes part of the slit. In another embodiment eachring-shaped element comprises its own separate slit whereby the devicecomprises separated rings.

[0264]FIG. 21 shows an elevational perspective view comprising a doublering where 75 represents the slit of the upper part 72 and 76 representsthe slit of the lower part 73. Both of the slits 75 and 76 have asubstantially tongued course.

[0265]FIG. 22 shows a cross sectional perspective view of a curl-shapedembodiment of the device in which the slits 77 and 77 a extend throughthe entire device and contribute to the curl-shape.

[0266]FIG. 23 shows a sectional perspective view of a curl-shapedembodiment of the device or a double ring in which the surfaces of thering elements which are in contact with each other have a surfacepattern preventing the rings from sliding apart. In the embodimentshown, the pattern is represented by circular grooves which, as appearsfrom the cross sectional view 78, fit into each other.

[0267]FIG. 24 shows a cross sectional perspective view of a ring-formedembodiment of the device in which the passage for the ligament is in thecentre and in which the dimensions of the cross section areas of thering 79 are substantially the same.

[0268]FIG. 25 shows a cross sectional perspective view of a ring-shapedelement in which the hole or passage of the ring is placed eccentricallyand in which one part of the ring in a cross section 81 differs in sizefrom the corresponding part 80. The specific dimensions of such aring-shaped embodiment of the device may be individually adapted inaccordance with the anatomical conditions of the patient.

[0269]FIG. 26 shows a cross sectional perspective view of an embodimentof the device corresponding to the one seen in FIG. 16. However, in thisembodiment the slit 82 extends through each of the ring-shaped elementsand furthermore, the surfaces constituting the slit comprise grooveslocated in a substantially radial direction which thereby forms asubstantially zigzag course at the surface of central passage for theligament.

[0270]FIG. 27 shows a perspective view of an embodiment similar to theone shown in FIG. 26. The zigzag course of the slit 83, representingradially extending grooves which fit into each other, is clearly seen atthe outer surface of each of the ring elements constituting the device.However, the grooves need not extend completely from the inner to theouter surface of the device but may be present in located areas only.

[0271]FIG. 28 shows a cross sectional perspective view of a ring-shapedelement, e.g. corresponding to the lower part of the ring-shaped elementseen in FIG. 27. The grooves 84 extend from the periphery into thecentre 86 of the ring-shaped element 85.

[0272]FIG. 29 shows a perspective view of one embodiment of aninstrument with the prosthetic device 11 located between the upper part21 of the instrument facing the acetabulum (not shown) and the lower 22part of the instrument having a concave shape facing the femoral head 1.The prosthetic device 11 is placed around the femoral ligament 5 whenthe upper 21 and lower 22 parts of the instrument are allowed to open byoperating the handle 24 connected to the part 21 and the handle 23connected to the part 22. As appears from the drawing, the handles 23and 24 may be moved relatively to a common axis.

[0273]FIG. 30 shows a perspective view of the upper part of theinstrument as shown as 21 in FIG. 29 with a view into the concavesurface facing the convex surface of the lower part 22 shown in FIG. 29.Means for pushing 19 are shown which in one embodiment substantiallyhave the shape of a stirrup where the base pushes the prosthetic devicetowards the means 20 for opening the slit of the prosthetic device. Themeans 20 comprises a V-shaped incision 25 having elevated edges forminga wedge which forces the slit of the prosthetic device to open when theprosthetic device is pushed towards the wedge by the base portion of themeans 19. The slit of the prosthetic device is gradually widening whilebeing pushed by 19 towards the means 20 whereby the prosthetic devicecan be placed around the ligament which is fixed within the incision 25of the instrument. The incision 25 is shown as V-shaped, however anyother shape allowing the ligament to be situated in the slit is withinthe scope of the invention. The means 20 encompass any embodimentsuitable for placing the device around the ligament, accordingly, themeans could include a spring which separates the mating surfaces of theslit. The upper part 21 in FIG. 29 of the instrument may also comprisetwo moveable parts which together substantially form a concave cavitymating the lower part of the instrument shown as 22 in FIG. 29. Themovable parts may furthermore form an incision 25 by having partsseparated from each other. In addition, the movable parts may be able tooverlap and may comprise fastening means for the prosthetic device, e.g.for each side of the slit, so that when the movable parts are movedapart, the slit of the device is forced to open allowing the device tobe placed around the ligament. In a still other embodiment, the innersurface of the upper part of the instrument 13 comprises means foropening the slit of the prosthetic device which is operated separately,e.g. in form of a string or wire connected to the device on each side ofthe slit so that the slit can be opened by pulling the string. Asuitable direction of the pull can be secured, e.g. by fastening thestring to a suitable point at the periphery of the concave cavity 13,e.g. by letting the string to pass through an eyelet. The means 19 aswell as any string or wire may be operated by means extending throughthe handle 18.

[0274]FIG. 31 shows a sectional perspective view of an embodiment of theupper part of the instrument comprising an edge or wall of a V-shapedincision 12 of the inner surface 13. Pushing means 14 are connected to ahandle 15 positioned within the handle 16 of the upper part of theinstrument as also shown. The pushing means 14 have a base portion whichis adapted to the shape of the prosthetic device.

[0275]FIG. 32 shows a perspective view of the embodiment shown in FIG.31 but seen from above. The incision 25 enables the instrument to beplaced in the joint without impeding the function or anchoring ofligamentum femoris as this is situated between the “legs” of theincision.

[0276]FIG. 33 shows a perspective view of an embodiment of the upperpart of the instrument in which the pushing means 27 comprise means 28for securing the prosthetic device. The means 28 have the shape of ahook located on each leg of the pushing means which are adapted to guidethe prosthetic device. The prosthetic device is placed so that the outeror distal opening of the slit corresponds to the incision 25 of theinstrument, the hook 28 on each side may then be secured to the deviceon the corresponding side of the slit. Preferably, in this position, theslit is open to receive the ligament. When the handle 26 is pushedtowards the incision where the ligament is placed, the prosthetic devicewill be placed around the ligament, and the slit may then allow to closeas the hook on each side (holding the device) let go when the pushingmeans are moved further on. As appears from FIG. 33, the pushing meansmay be operated by a part located within the outer handle of the upperpart of the instrument which thereby functions as a guide.

[0277]FIG. 34 shows a perspective view of a scissors-like embodiment ofan instrument where 21 represents the upper part and 22 the lower partof the instrument. The prosthetic device is placed between those partswhen inserted into the joint. Incisions as well as pushing means asdescribed for the embodiments above may also be present.

[0278]FIG. 35 shows a perspective elevational view of a hip joint. Thefemoral head 1 has been retracted from the acetabulum 8 giving a spacein the joint of approximately 1-2 cm. The outer surface of the upperpart of the instrument 17 having a handle 24 is placed on the femoralhead 1. The lower part of the instrument (not seen) is present withinthe upper part 17, the ligament 5 is located in the correspondingincisions (not seen) of the lower and upper part 17 of the instrument.

[0279]FIG. 36 shows a view similar to the one is FIG. 35 in which thehandle 23 of the lower part of the instrument is now seen above thehandle 24 of the upper part 17 of the instrument. The prosthetic devicelocated between the upper and lower part 22 of the instrument may now bepushed towards the ligament 5 as the upper and lower part 22 of theinstrument are now let open by operating the handles 23 and 24.

1. A prosthetic device for insertion into a joint cavity of a joint of avertebrate, such as a human, said device consisting of a biocompatiblematerial comprising at least a first polymeric component and a secondpolymeric component, wherein the chain length of the first polymericcomponent is longer than the chain length of the second polymericcomponent.
 2. The prosthetic device according to claim 1, wherein thefirst polymeric component has a carbon-backbone.
 3. The prostheticdevice according to claim 1 or 2, wherein the first polymeric componentand the second polymeric component are compounded to form a bidispergentsystem.
 4. The prosthetic device according to claim 1, wherein the firstpolymeric component is selected from polyacrylates, polystyrene,polyethers, polytetrafluorethylene, polyvinylalcohol, polyethylene, andpolypropylene.
 5. The prosthetic device according to any of thepreceding claims, wherein the second polymeric component is selectedfrom polyacrates, polystyrene, polyethers, polytetrafluorethylene,polyvinylalcohol, polyethylene, and polypropylene.
 6. The prostheticdevice according to any of the preceding claims, wherein the secondpolymeric component is cross-linked.
 7. The prosthetic device accordingto any of the preceding claims, wherein the first and the secondpolymeric component comprises the same monomeric component.
 8. Theprosthetic device according to any of the preceding claims, comprising athird polymeric component, said third polymeric component beingdifferent from the first and/or the second polymeric component.
 9. Theprosthetic device according to claim 8, wherein the third polymericcomponent is selected from polyethylene oxides, and polyvinylpyrrolidon.10. The prosthetic device according to any of the preceding claims 8 or9, wherein the third polymeric component is grafted to the first and/orthe second polymeric components.
 11. The prosthetic device according toany of the preceding claims, wherein the chain length of the firstpolymeric component is above 100 monomer units.
 12. The prostheticdevice according to claim 1, wherein the first polymeric componentcomprises a copolymer of polyethylene and polypropylene, and the secondpolymer is grafted to the first polymer.
 13. The prosthetic deviceaccording to claim 1, wherein the first polymeric component is across-linked polymer, and the second polymer is grafted to the firstpolymer.
 14. The prosthetic device according to claim 12, wherein thesecond polymeric component is selected from polyethylene oxides, andpolyvinylpyrrolidon.
 15. A prosthetic device for insertion into a jointcavity of a vertebrate such as a human, wherein the body of the devicecomprises a polymer material, and wherein the device comprises a holeextending through the body of the device.
 16. A prosthetic deviceaccording to claim 2, wherein the device further comprises a slit in thebody of the device extending through the body of the device from thesurface of the body to the hole.
 17. A prosthetic device according toclaim 2, wherein the device further comprises a means of enabling apassage through the body of the device to the hole.
 18. A prostheticdevice according to any of the preceding claims, wherein said device isadapted to alleviate conditions associated with worn cartilage byproviding a spacer function and/or to exert pressure distribution in thejoint when the joint is loaded and/or to provide at least part of thesliding/rotating movement of the joint by internal movement of at leastpart of the device.
 19. A prosthetic device according to any of thepreceding claims, wherein the device is capable of locking itself to anintra-articular component and thereby being fixed or retained in thejoint cavity in a manner which is substantially non-invasive withrespect to cartilage and bone natively present in the joint cavity. 20.A prosthetic device according to any of claims 1 or 2, wherein thepolymer material is obtained by cross-linking polyethylene,polypropylene or polyvinylpyrrolidone or combinations or co-polymersthereof.
 21. A prosthetic device according to claim 7, wherein thecross-linking is achieved with radiation.
 22. A prosthetic deviceaccording to claim 8, wherein the forms of radiation are selected fromthe group comprising high-energy electrons, gamma rays, photons,microwaves, and thermal radiation.
 23. A prosthetic device according toany of the preceding claims, wherein the polymer material meetsmechanical properties in that the E modulus (Young's modulus) is atleast 10 MPa.
 24. A prosthetic according to any of the preceding claims,wherein the device comprises more than one more unit.
 25. A prostheticdevice according to claim 11, wherein the units are adapted not tointerfere with intra-articular components when the device is in thejoint cavity.
 26. A prosthetic device any of the according to claim 11,wherein the body of the unit further comprises a hole extending throughthe body of the device.
 27. A prosthetic device according to claim 13,wherein the body of the unit further comprises a slit extending from thesurface of the body to the hole.
 28. A prosthetic device according toany of the preceding claims, wherein the polymer is subjected or furthersubjected to surface treatment to obtain optimised wetting ability andto obtain biocompatibility and resistance to heat treatment forsterilisation.
 29. A prosthetic device according to claim 15, whereinthe surface treatment results in a material with critical surfacetension (γ_(c)) values within the “zone of biocompatibility” of 20-30dynes/cm.
 30. A prosthetic device according to any of the precedingclaims, which is capable of locking itself to the intra-articularcomponent by at least one element of the device surrounding thecomponent in such a manner that displacement of the element is limitedby interlocking with said component.
 31. A prosthetic device accordingto claim 30, wherein the element completely or substantially completelysurrounds an intra-articular component being a ligament.
 32. Aprosthetic device according to any of the preceding claims, whichdevice, when present in situ, comprises at least one ring-shapedelement.
 33. A prosthetic device according to any of the precedingclaims for the articulation of a hip of a human, which device is adaptedso that it, when present in situ in the human hip joint cavity,comprises at least one element surrounding ligamentum capitis femoris.34. A prosthetic device according to any of the preceding claims, inwhich the element which is adapted to surround the ligament when presentin situ, has such a shape and such properties that it can be placedaround the ligament and, when placed around the ligament, will stayinterlocked with the ligament.
 35. A prosthetic device according to anyof the preceding claims which is a hip endoprothese and wherein theelement has a shape and properties permitting arranging the elementaround ligamentum capitis femoris.
 36. A prosthetic device according toany of claims 30-35, wherein the element, when present in situ, permitsthe ligament to extend through the element and substantially exert itsnatural function on the joint.
 37. A prosthetic device according to anyof the preceding claims, having such shape and/or properties that it iscapable of replacing or supplementing worn or damaged cartilage in thejoint and/or is capable of preventing wear of the native cartilage ofthe joint.
 38. A prosthetic device according to any of claims 30-36,wherein the element surrounding the intra-articular componentconstitutes the device.
 39. A prosthetic device according to any of thepreceding claims wherein the shape of the device mating the load bearingpart of the joint is substantially circular.
 40. A prosthetic deviceaccording to claim 39, wherein the diameter of the device in situ andwhen the joint is loaded is such that it substantially covers thesurface area of the load bearing part of the joint which in the normaljoint is covered with cartilage.
 41. A prosthetic device according toclaim 40, wherein the joint is the hip joint, and wherein the diameterof the device is such that the surface of caput femoris is substantiallycovered when the joint is loaded.
 42. A prosthetic device according toclaim 39, wherein diameter of the device is between 15-80 mm, such asbetween 25-70 mm, preferable between 30-60 mm, more preferable between35-50 mm, most preferred about 40 mm, when the joint is loaded.
 43. Aprosthetic device according to any of the preceding claims, wherein thethickness of the device is between 2-60 mm, such as between 6-40 mm,preferable 8-30 mm, more preferable about 10-20 mm, most preferableabout 15 mm in the unloaded stage.
 44. A prosthetic device according toany of the preceding claims, wherein the device comprises partsoverlapping each other.
 45. A prosthetic device according to claim 44,wherein the overlapping parts, on their mating surfaces have aninterlocking surface structure.
 46. A prosthetic device according toclaim 45, wherein the interlocking surface structures constitutegrooves.
 47. A prosthetic device according to claim 46, wherein theinterlocking surface structures are grooved in a radial direction.
 48. Aprosthetic device according to claim 46, wherein the interlockingsurface structures are grooved in a circular direction.
 49. A prostheticdevice according to claim 45, wherein the interlocking surfacestructures constitute elevations and corresponding depressions.
 50. Aprosthetic device according to any of the preceding claims, wherein theE modulus (Young's modulus) of the material of at least part of thedevice is at least 10 MPa, such as at least 13 MPa, preferably at least16 MPa, more preferable at least 19 MPa, still more preferable at least22 MPa, most preferable at least 25 MPa, such as at least 30 MPa or 50MPa.
 51. A prosthetic device according to any of the preceding claims,wherein the material constituting the device comprises polypropylene,preferably cross-linked polypropylene.
 52. A prosthetic device accordingto claim 32, wherein the ring-shaped element has a shape of a horseshoe,a torus, or a curl.
 53. A prosthetic device according to claim 52,wherein the ring-shaped element has an upper convex shape and a lowerconcave shape.
 54. A method for introducing a prosthetic device into ajoint comprising locking the device to an intra-articular component,thereby fixing or retaining the device in the joint cavity in a mannerwhich is substantially non-invasive with respect to cartilage and bonenatively present in the joint cavity.
 55. An instrument for inserting aprosthetic device according to any of claims 1-53, comprising means fordeforming the prosthetic device into a reduced volume or a slender shapeand means for grasping the intra-articular component to which the deviceis capable of interlocking.
 56. The use of a prosthetic device forestablishing slidability and/or distributing pressure in a joint of avertebrate such as a human, by inserting into the joint cavity of thejoint a prosthetic device, preferably a prosthetic device as defined inany of the claims 1-53, capable of locking itself to an intra-articularcomponent and thereby being fixed or retained in the joint cavity in amanner which is substantially non-invasive with respect to cartilage andbone natively present in the joint cavity.
 57. A method for establishingslidability and/or pressure distribution in a joint of a vertebrate suchas a human, comprising inserting into the joint cavity of the joint, aprosthetic device, preferably a prosthetic device as defined in any ofthe claims 1-53, which is capable of locking itself to anintra-articular component and thereby being fixed or retained in thejoint cavity in a manner which is substantially non-invasive withrespect to cartilage and bone natively present in the joint cavity. 58.A kit comprising: a) an intra-articular prosthetic device for a jointhaving a.1) a spacer function and/or capability to exert pressuredistribution and/or sliding/rotating movement of the joint by internalmovement of the device by means of a resilient member, and a.2) alocking mechanism adapted to fix the device to an intra-articularcomponent by means of an element of the device surrounding the componentin such a manner that displacement of the device is limited byinter-locking with the component; and b) an instrument for inserting theprosthetic device into a joint cavity.
 59. The kit according to claim 58wherein the instrument of b) comprises one or more of the followingmeans b.1 to b.4: b.1.) means for deforming the prosthetic device into areduced volume or to a slender shape and keeping this volume or shapeupon introduction of the device to the joint, b.2.) means for graspingor encircling the intra-articular component to which the element of theprosthetic device is capable of inter-locking, b.3.) means for leavingthe prosthetic device in the joint with the element of the prostheticdevice surrounding the intra-articular component.
 60. A kit according toclaim 58 or 59, wherein the instrument further comprises a handle.
 61. Akit according to claim 59, wherein one or more of the means of b.1.),b.2.), and b.3.) are connected to or forms part of a handle.
 62. A kitaccording to any of claims 58-61, wherein the resilient member of a.1)and the element surrounding the intra-articular component of a.2)constitutes a solid prosthetic device.
 63. A kit according to any of theclaims 58-62, wherein the intra-articular prosthetic device is asdefined in any of the claims 1-53.